1. Field of the Invention
The present invention relates to computer-assisted surgery systems and, more particularly, to instrumentation used for the tracking of surgical tools during computer-assisted surgery.
2. Background Art
Tracking of surgical instruments or tools is an integral part of computer-assisted surgery (hereinafter CAS). The tools are tracked for position and/or orientation in such a way that information pertaining to bodily parts is obtained. The information is then used in various interventions with respect to the body, such as bone alterations, implant positioning, incisions and the like.
Two types of tracking systems are commonly used. The active tracking systems provide a transmitter on the tool to be tracked, which transmitter emits signals to be received by a processor of the CAS system, which will calculate the position and/or orientation of the tool as a function of the signals received. The transmitters of the active tracking systems are powered, for instance by being wired to the CAS system or by being provided with an independent power source, so as to emit signals.
Passive tracking systems do not provide active transmitters on the tools, and therefore represent fewer issues pertaining to sterilization. The CAS system associated with passive tracking has an optical sensor apparatus provided to visually detect optical elements on the tools. The optical elements are passive, whereby no power source is associated therewith.
In order to obtain values for position and/or orientation, the optical elements must be in the line of sight of the optical sensor apparatus. Accordingly, with passive tracking systems, surgery takes place in a given orientation as a function of the required visibility between the optical sensor apparatus and the optical elements.
In a known embodiment, the optical elements are retro-reflective spheres detectable by the optical sensor apparatus of the CAS system. The retro-reflective spheres are positioned in a recognizable pattern, such that position and/or orientation information of the tool associated with the optical elements is calculable. The geometry of the retro-reflective spheres advantageously offers a good range of visibility. However, the retro-reflective spheres are relatively costly to produce.